Component of the FTS/Hook/FHIP complex (FHF complex) (PubMed:18799622, PubMed:32073997). The FHF complex may function to promote vesicle trafficking and/or fusion via the homotypic vesicular protein sorting complex (the HOPS complex) (PubMed:18799622). FHF complex promotes the distribution of AP-4 complex to the perinuclear area of the cell (PubMed:32073997). Required for spermatid differentiation. Probably involved in the positioning of the microtubules of the manchette and the flagellum in relation to the membrane skeleton (By similarity). {ECO:0000250|UniProtKB:Q8BIL5, ECO:0000269|PubMed:18799622, ECO:0000269|PubMed:32073997}. This is the function of ENSG00000134709 (HOOK1, hook microtubule tethering protein 1).